Refuse what's not on approved list, initially (5)
I believe the answer is:
offal
'refuse' is the definition.
(thesaurus)
'not on approved list initially' is the wordplay.
'not on' becomes 'off' ('off' is the opposite to 'on').
'initially' suggests taking the first letters.
The initial letters of 'approved list' is 'al'.
'off'+'al'='OFFAL'
'what's' is the link.
(Other definitions for offal that I've seen before include "Heart, liver, kidney etc" , "Putting cargo on (ship)" , "Animal entrails and internal organs as rubbish" , "Less valuable edible parts of animal" , "Waste of carcase" .)